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Site Assessment Report 1022 Frontage Road C A M B R I A Ripon, California • December 16, 2005 six out of the 10 soil samples at concentrations ranged from 3 4 to 5,100 mg/kg Benzene was detected in three out of the 10 samples at concentrations ranging from 0 022 to 0 12 mg/kg July]998 In July 1998,Walton installed anew gasoline UST,ten dispensers(eight diesel and two gasoline dispensers), and new product piping to connect the new dispensers with the new gasoline UST and existing diesel ASTs September 1998 In September 1998, Walton removed three steel, single wall USTs, (7,500 gallon and 10,000 gallon gasoline USTs and one 12,000 gallon diesel UST),four additional dispensers,and associated piping Twenty-four soil samples (T1 through T3, FD7 through FD10, and PL5 through PL17) were collected by Grayland during the UST,dispensers,and piping removal activities TPHd concentrations ranged between<1 0 and 12,000 mg/kg(FDIO) TPHg concentrations ranged between <1 0 and 1,500 mg/kg(T2n) Benzene concentrations ranged between<0 005 and 2 3 mg/kg(T3n) " As a result, Grayland Environmental recommended that additional assessment be conducted to evaluate the extent of hydrocarbon-impacted soil and to determine if groundwater beneath the site was impacted A total of approximately 1,180 tons (600 cubic yards)of hydrocarbon-impacted soil was removed from the site and disposed of at Forward Landfill in Stockton, California 47and MaytoAugust]999 BetweenMayand st 199,AGE oversaw the advancement of soil borings B 1 through B 16,hydropunch borings HP HP18 and the installation of groundwater monitoring wells MW-1 through MW-5 Soil samples were collected at 5-foot intervals from each of the borings and select samples were submitted to the laboratory for analysis Based on the analytical results, it was determined that the greatest hydrocarbon-impact to soil was in the area immediately adjacent to the former USTs at 20 ft bgs Hydrocarbon-impacted soil appeared to be limited to a depth of approximately 30 ft bgs The highest TPHg concentration was detected in the 20 foot sample from baring B5(1,300 mg/kg)and the highest TPHd concentration was detected in the 20 foot sample from boring B4(8,200 mg/kg) The highest benzene concentration was detected in the 20 foot sample from boring B4(2 6 mg/kg) The highest methyl tertiary-butyl ether(MTBE)concentration was detected in the 10 foot sample from boring B I (12 mg/kg) Grab groundwater samples were collected fromo- bormgs B2,B5, B14, HP17, and HP18 Dissolved-phase hydrocarbons extended north and west of the former USTs TPHg and benzene concentrations appeared to attenuate east and south of the former 'r° e Je1m USTs(AGE, 1999) The highest dissolved-phase TPHd,TPHg,benzene,and MTBE were detected ate v i� 04 concentrations of 580,000, 23,000, 370, and 2,900 µg/L, respectively, in boring B2 located on the south side of the former USTs ' 40, Pch%002 In 1V�r"nh002,AGE oversaw the installation of groundwater monitonng well MW-9 and extraction well EW-1 Well EW-1 was installed in preparation for an aquifer pump test Soil 4